Plant for the production of compressed air



Jan. 30, 1951 c. KELLER 2,539,744

PLANT FOR THE PRODUCTION OF COMPRESSED AIR Filed Aug. 8, 1945 lnvantor Akkornegi:

Patented Jan. 30, 1951 PLANTF-OR THE PRODUCTION OF COMPRESSED AIR Curt Keller, Kusnacht, Switzerland, assignor to Aktiengesellschaft Flier Technische Studien, Zurich, "Switzerland, a corporation of Switzerland Application August 8, 1945, Serial'Nc..;609,67 9 In Switzerland August 12,1944

ACIairns.

This invention relates to a plant for the productionof compressed air, for example blast'furnaceair, in which air is brought in atleast one compressor "to a higherpressure than that cor responding to the pressure at which 'it is to be used, then heated in a heater by an indirect supply of heat derived'froman external sourceand ,hereupon expanded whilst giving upenergy in at least one turbine which drives the compressor. The object of the invention is to provide a plant of tnis'kind in which the consumption of energy and of heat 'per normal cubic metre of oompressed' air is small and which realizes by simple cornbustional means an economical improvement in comparison with hitherto existing'plants.

The invention baseson the fact that acornparatively large amount of heat is still contained in -the exhaust air of the turbine. Now, the .eificiency of plants ofthe type inxquestion is higher, the higher the degree to which it is possibleto utilizethe heat-content of .the exhaust air of the plant without it being necessary to provide, for example, heat exchangers -.of large .dimensions. For this purpose in a plant according to the present invention aportion of the quantity of air drawn in by the compressor is branched oif in any case not later than before the last .stage of the turbine and is delivered to a consumer .of compressed .air, while the remaining portion of said quantity of air, after having passed through the turbine, enters the heater, at least partially, as a r for combustion purposes.

The accompanying drawing illustrates by way of example and in a simplified form of representation a preferred arrangement according to this invention. In this drawing the figure shows a infant in which the compressed air required in a blast furnace is branched off from a pine connecting the two casings of a two-casing air turbine.

Referring .to the draw'ing,the numerals I and [indicate the casings of a two-casing compressor which draws in air from the atmosphere. This air, which is cooled between. the two casings I, 2 in a cooler 3, is compressed above "the pressure which is required in a consumer of compressed air which, in the example shown, is a blast furnace connecting the two casings of the compressor 5, 2., The air compressed by the compressor I, '2 passes first into a heating system of a heater 6;, to which external heat, derived for example from the combustion of blast furnace gas, is suppliedinanindirect manner. Thenumeral- I de notes a'burne'r of theheater- Gto fuelis 4. The reference .3 denotes a pipe 2 supplied through a pipe 8. The air heated the heating system 5 passes into the high-pressure section 9 0i a two-casing turbine, whereinrit expands w iilegivin-g up energy, and passes hereupon through a connecting pipe 9 into the low pressure section 9 of the turbine-where 'it iurther expands. The energy produced in the turbi-ne fiyt serv-es to drive the compressor l, '24 A possible excess of energy produced in the turbine 8,- canbe transferred to a machine 9" designed as a motor-generator which can supply anyzsupplenientary energy which may possibly be required to :drive'the compressor I, 2 and if need ban-lay serve as a booster for thema'chine group L2 and 9,9 when starting up. A portion :or the quantity of air drawn in by the compressor 1, 2 and expanded in the high-pressure section 8 .of the turbine is branched off at the point :8 of the connecting pipe 9 and passes by of a heating system I, which is likewise arranged within the heater Sand in which external heat is supplied indirectly to said air portion, into the blast furnace 4, The greater part of the remaining portioniof' the quantity of air drawn in, which traverses the whole of the turbine S, 9 passes through a pipe II to the burner I of the heater 6 where thisair serves as combustion air. Fuel is supplied to the'burner "I through a pipe -8. Thus "a portion of the quantity of air drawn in by the compressor I, i2 is branched 01f in any case not laterthan "before the "last stage of the low pressure Secti0n'9' of the turbine and passed into the blast furnace A, while the greater part of the -re-,-

maining portiono'f said quantity ofair after passing throughboth turbine sections 9, 8 flows as combustion air to the burner "l of the heater-.6. In the embodiment shown in this Fig. 1 the expansion of the quantity of air which remains after theair required in. the blast furnace 4 has been branched on at the point 9 takes place a separate turbine, i. e. in the low-pressure 'sec-' tion 8' Furthermore, the supply of all external heat takes pace in a' sole heater 6, and the cornp-reSsion of all theair required for consumption purposes "and for driving the plant takes place in a common "two-casing compressor I, 2. BY

means of a valve 3 inserted :in the pipe 3 for supplying cooling water to the. intermediate cooler the degree of intermediate cooling may beinfiuenced when the quantity of air required by theblast furnace l'varies, in such .asmanner that the compression takes place either isothermi'cally oriadiabatically to 'a greater or lesser degree. By :meansofra valve 9 inserted in the quantity cf: aha-expanded connecting pipe 9 -the in the low-pressure turbine 9 can be varied when the quantity of air required for consumption varies, and by means of a valve 8 inserted in the fuel supply pipe 8 the degree of heat supplied to the air passing into the high-pressure section 9 and into the low-pressure section of the turbine may be varied when the quantity of said air required for consumption varies. An adaptation of the power taken up by the compressor I, 2 and f the energy produced by the turbine 9, 9 to the quantity of air required for consumption in the blast furnace 4 or to the pressure up to which the air has to be compressed, may also be attained by providing for a varying quantity of air to by-pass either the high-pressure section 2 of the compressor or the low-pressure turbine 9 or even both these two machines. For this purpose a pipe section 3 is employed which connects the pipe 3 provided between the two casings of the compressor I, 2 with the delivery pipe 2 of the high-pressure sect on 2 of the compressor, a valve 3 being inserted in said pipe section 3 Moreover, for the same purpose a pipe section 9 is provided which connects the pipe 9 arranged between the two casings 9, 9 of the turbine with the exhaust pipe H of the low-pressure section 9 of the turbine and in which a valve9 is inserted. Final y, when the quantity of air requ red for consumption varies or the pressure of the compressed air has to be varied, the speed of the machine groups I, 2 and 9, 9 can also be varied. Of the hereinbefore mentioned different steps to be taken when the air required for consumption varies or the pressure of the compressed air has to be varied, several or all of them may be adopted at the same time.

Under certain circumstances it may be of advantage t branch off a portion of cxpanded air passing from the low-pressure section 9 of the turbine into the p pe H at a point of the latter and to introduce thi port on into a preheater 8 for the fuel pa s ng through the ipe 8 into the burner 1. A portion of the ex anded air which has passed int the pine l I may also be introduced through a pine H into a heat exchanger H in which is preheated the compressed air which passes from the high-pressure sect on 2 of the compressor through the pipe 2 into the heating syst m 5.

The illustrat d embodiment of tho in ention is a plant for heating the consumption air supplied to the blast furnace 4 and for heating the motive air supplied to the turbines 9, 9', which drive the compressor I, 2. A useful feat re of the arrangement is that the air for each of the two stat d purpo es s heated in a single h ater 6.

The quantity of exhaust air flowing from the turbine to the burners and used for combustion purposes can be and desirably is at least twice the quantity of air re uired for complete combustion in the heater 6,

A plant to supplv blast air to a blast furnace must be capable of operating cconomically under normal conditions of operation and must also be capable of furnishing air at higher pressure, say

twice the normal pressure, under abnormal conditions which occur only seldom, for example, conditions occasioned by hanging of the charge. The illustrated plant can be operated so as to meet such requirements, as will now be explained. Turbines and turbo-compressors devolop good efiiciency only at normal speeds and in any plant of the type illustrated, a serious problemi's presented when the plant must furnish blast air at a higher than normal pressure.

The; illustrated plant can be operated under normal conditions with the valve 9 closed and the valve 9 wide open that the second turbine 9' is completely by-passed. As a consequence, the air supplied through the pipe i I to the heater 8 and, as combustion air to the burner I, is relatively hot because it has not been expanded through the second turbine 9'. For this reason the valve 8 which controls the delivery of fuel to the burner would be about half closed. If a condition should arise in the blast furnace 4 requiring a higher blast pressure, the valve 9 would be opened and the valve 9 would be closed. At the same time the fuel valve 8' would be opened more widely, to compensate for the fact that the air supplied through the pine II has been expanded through the second turbine and consequently brings less heat to the burner.

The efiects of these adiustments are numerous and are inter-related. The pressure at the point 9 r ses so that the blast pressure increases which, of course, is the primary efiect sought. In addition the spe d of the machine set I, 2, 9, 9', 9" increases so that the compressors i, Z deliver at increased pressure.

It will be observed that the opening of the valve 8' incr ases the amount of combustion gas to be burned in th y burn r 1 but this circumstance imposes no difliculty despite the fact that a larger proportion of the a r tapped off at 9 flows to the blast furnace. The reason for this is that, as stated above, the system operates normally with an excess quant ty of combustion air, i. e. at least twice the ouantity required, so that even when the amount of gas b rned is increased, the combustion air is more than ample.

It will be observed that the effects produced by the valves 3 9 and 8' are clo ely related and affect not merely the flow path through the second turbine but also the total combustion fuel suppl ed to the sy tem and the supply of heat through the co bust on air and through the fuel pre-heater to the system.

The invention thus affords a flexible turbinedriven syst m wh ch can be designed to operate at its maximum efficiency under normal conditions with the second turbine 9' cut out. It also will operate with acceptable efliciincy at h gh speed un er abnormal con itions with the second turbine 9 included in the circuit. Its inclusion reduces the'temperature of the combust on air and reduces the quantity of combustion air, but not below a safe min mum. In addition, the valve 3 and the valve 3 which control the inter-cooler, permit regulation of the performance of the second compressor 2 should that be necessary as a c n equence of chang d operating conditions and the changed speed of o eration of the machine units as above mentioned.

The design of such components as the compressors, the heater for the combustion air and the driving air may be varied to a considerable extent. It is pertinent toremark that the expression combustion air is used in a generic sense to include both primary air and secondary air which may be supplied to the heater. It should be observed that the increased back pressure developed when the second turbine 9 is cut into the circuit can be used as the effective means for increasing the pressure on the consumption air. Thus, the valves 9 and 9 have two important functions. They control the speed of the machine set to establish two different conditions and they control the pressure under which 1. A plant for the production of compressed air,

comprising in combination, staged turbo-compressor means arranged to compress air to a pressure higher than that at which it is to be used; a combustion heating means arranged to supply heat to air so compressed, said heating means being of a type in which products of combustion are segregated from the heatcd air; means for varying the quantity of fuel supplied to said heating means; a preheater for heating said fuel; two turbines in which air so heated is expanded while giving up energy, said turbines being connected to drive the compressor means; a flow connection leading from the first to the second turbine; an exhaust connection for said second turbine arranged to deliver both combustion air to said heating means and heated air to said-pre heater; a by-pass branched off said flow connection and leading into said exhaust connection; a shut-off device in said by-pass controlling the passage of air therethrough; a second shut-01f device in said flow connection controlling the supply of air to saidsecond turbine; and a discharge connection for a part of said air, leading from a point in said flow connection between the outlet of said first turbine and said two shut-off devices, to a point of use.

2. The combinationdefined in claim 1 including a by-pass leading around stages of the turbocompressor means; and means serving to control flow through said by-pass.

3. The combination defined in claim 1 including an intercooler interposed between compression stages; a by-pass leading around a portion of the stages of said turbo-compressor means and around said intercooler; and means for controlling flow through said by-pass.

4. A plant for the production of compressed air, comprising in combination, staged turbocompressor means arranged to compress air to a pressure high r than that at which it is to be used; combustion heating means arranged to supply heat to the air so compressed, said heating means being of a type in which products of combustion are segregated from the heated air; means for varying the quantity of fuel supplied to said heating means; two turbines in which air so heated is expanded while giving up energy, said turbines being connected to drive said compressor means; a flow connection leading from the exhaust of the first to the inletof the second turbine; an exhaust connection leading from the exhaust of the second turbine to the burner for delivering combustion air to the latter; valve means operable to close the inlet to the second turbine and connect said flow connection with said exhaust connection; and a discharge connection for a part of said air leading from a point in said flow connection between the exhaust of the first turbine and said valve means.

CURT KELLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

